Question: What exactly is 'strange' matter, and anti-matter - what are their properties, and how to they affect our universe. Also, is there any relationship between them and dark matter.

James M Monk answered on 17 Jun 2011:

Normal protons and neutrons are made up of “up” and “down” quarks, but there are other types of quarks – we know of 6 types in total. In the same way that the muon is just a heavier version of an electron, a strange quark is just a slightly heavier version of the down quark. So you can get things like protons or neutrons where (one of) the down quarks is replaced with a strange quark.

Such “strange” particles usually decay quickly because of the extra mass, but some people have suggested that neutron stars (which are like giant atomic nuclei) could be made of this “strange” matter in some cases. There is not any evidence for it though (and I’m not sure how you would obtain any).

Anti-matter is like normal matter, but all of the charge quantum numbers are the negative of everyday matter. So an anti-electron (or positron) has the same mass and spin quantum numbers as an electron, but opposite charge.

Neither strange matter nor anti-matter provides a dark matter candidate. Anti-matter would interact with normal matter, so we would be able to see it if it were there. Strange matter would also interact with normal matter.